1. Field of the Invention
The present invention relates generally to specimen inspection and review. More particularly, the present invention relates to abeam inspection and systems.
2. Description of the Background Art
Automated inspection and review systems are important in process control and yield management for the semiconductor and related microelectronics industries. Such systems include optical and electron beam (e-beam) based systems.
An example of an e-beam apparatus for an inspection or review system is described in U.S. Pat. No. 5,578,821, issued to Meisberger et al (the Meisberger patent). The disclosure of the Meisberger patent is hereby incorporated by reference in its entirety. FIG. 1 (corresponding to FIG. 5 in the Meisberger patent) is a simplified schematic representation of the paths of the primary, secondary, back-scatter and transmitted electrons through the electron column and collection system for electron beam inspection. In brief, FIG. 1 shows a schematic diagram of the various electron beam paths within the column and below substrate 57. Electrons are emitted radially from field emission cathode 81 and appear to originate from a very small bright point source. Under the combined action of the accelerating field and condenser lens magnetic field, the beam is collimated into a parallel beam. Gun anode aperture 87 masks off electrons emitted at unusable angles, while the remaining beam continues on to beam limiting aperture 99. An upper deflector (not depicted) is used for stigmation and alignment, ensuring that the final beam is round and that it passes through the center of the objective lens 104 comprising elements 105, 106 and 107. A condenser lens (not depicted) is mechanically centered to the axis defined by cathode 81 and beam limiting aperture 99. The deflection follows the path shown, so that the scanned, focused probe (beam at point of impact with the substrate) emerges from the objective lens 104. In High Voltage mode operation, Wien filter deflectors 112 and 113 deflect the secondary electron beam into the secondary electron detector 117. When partially transparent masks are imaged, the transmitted beam 108 passes through electrode system 123 and 124 that spreads the beam 108 before it hits the detector 129. In Low Voltage mode operation, the secondary electron beam is directed by stronger Wien filter deflections toward the low-voltage secondary electron detector 160 that may be the same detector used for backscatter imaging at high voltage. Further detail on the system and its operation is described in the Meisberger patent.
There are also other types of e-beam tools for inspection or review. For instance, another type is described in U.S. Pat. No. 5,973,323, issued to Adler et al (the Adler patent). The disclosure of the Adler patent is hereby incorporated by reference in its entirety. The Adler patent discloses a Secondary Electron Emission Microscope (SEEM). The SEEM is an example of a projection type system, where the e-beam impinges upon a relatively large region, and scattered electrons from the region are imaged onto a two-dimensional detector.